The Best Australian Science Writing 2014 Page 10
To build a record of how temperature changed in the past, we measure the proportion of heavy versus light water molecules, or isotopes, in the ice. Isotopes are versions of the same element that have different numbers of neutrons, and so have different masses. In ice we measure the number of water molecules that have a heavy hydrogen atom (deuterium, with an atomic mass of 2) compared to those with the light hydrogen atom (atomic mass of 1). The heavy molecules take more energy to move through the water cycle, and in warm climates more of these heavy molecules will reach Antarctica and fall as snow. So the proportions of these molecules act as a ‘thermometer’ for the past.
The isotopes in the James Ross Island ice core tell us the coolest time on the Antarctic Peninsula was around 600 years ago. Back then the climate was around 1.6° Celsius cooler than today. The ice also confirms that the warming here since the 1920s has been exceptionally fast – faster than at almost any other time in the past thousand years.
But this particular ice core reveals much more about the changing climate on the Antarctic Peninsula. James Ross Island is a ‘Goldilocks’ location for exploring the connection between temperature and ice melt. It is not so cold that summer temperatures are never high enough for melting to occur, and neither is it so warm that extensive melting destroys the climate record locked in the ice. Serendipitously, conditions on this ice cap are just right for preserving a rare history of summer ice melt.
The 1.6° Celsius of warming over the past 600 years may not sound significant, but it’s caused a tenfold increase in the amount of summer melting on James Ross Island. Most of this intensification of ice melt occurred in the past few decades. This unique history of summer ice melt is a powerful illustration of how environmental changes in a warming climate don’t always occur gradually.
Ice melt is an example of a threshold in Earth’s environment. When summer temperatures remain below 0° Celsius, no melting occurs. But as the climate warms towards this threshold, on some days in summer the temperature will go above 0° Celsius and there will be excess energy to melt the surface snow. Any further warming will increase the number of days that go over the melting threshold, and increase the level by which they exceed it. In this way, a small increase in average temperature can cause a large increase in melting.
So are images like the Larsen B ice shelf collapse evidence for recent climate change? Measurements from the ice core say they are. It shows us that rising temperatures have taken summer ice melt on the Antarctic Peninsula to a level unprecedented for at least the past thousand years. Ice melt is a critical process that weakens the structure of ice shelves and glaciers, and satellite images show that extensive summer melting caused the visually dramatic Larsen B collapse. Ice melt also has real implications for rising sea levels across the world.
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Rising sea levels in a warming world are particularly relevant to Australia as large proportions of our population and infrastructure are near the coast.
In 2013, the IPCC released its fifth assessment report. On our current emissions trajectory it projects that sea level is likely to rise by between 0.53 and 0.97 metres by 2100. This projection takes into account the thermal expansion of the oceans as they warm, as well as changes in snowfall, surface melting and glacier loss that will alter the quantity of ice locked up on land. What these model-based projections aren’t yet able to assess is the possibility of accelerating ice flow and loss from Antarctica’s vast ice sheets.
Antarctica’s contribution to sea level is a balancing act between ice accumulation across the central plateaus and ice loss around the margins of the continent. Satellite monitoring of Antarctica’s ice sheets over the past few decades has revolutionised our understanding of this changing balance. These satellite measurements use changes in the height or gravitational pull of the ice sheets to identify places where Antarctica is gaining or losing ice.
Overall, Antarctica is losing ice, accounting for just under 10 per cent of the rise in global sea level over the past two decades. The mountain glaciers and ice caps along the Antarctic Peninsula are losing around 20 billion tonnes of ice yearly. Even more significant is the approximately 65 billion tonnes of ice lost each year from West Antarctica.
This is just the tip of the iceberg, so to speak. West Antarctica has been described as the ‘weak underbelly’ of Antarctica’s ice sheets. This ice sheet sits on bedrock, but that ground is below sea level – by more than 2 kilometres in some places. This makes the ice sheet vulnerable to melting from beneath. As the margins of the West Antarctic Ice Sheet melt and thin, seawater warm enough to melt the ice is able to encroach further under the ice sheet, and this could cause ice to be lost even faster. The latest IPCC report flags the possibility that rapid collapse of parts of the West Antarctic Ice Sheet could cause sea level to rise substantially above current projections.
Earth’s past provides some evidence to gauge how quickly ice could be lost from Antarctica in the future. The last time the Earth’s temperature was similar to today – around 125 000 years ago – sea level was roughly 6 metres higher and changed twice as fast as the sea-level rise we’ve seen in the past decade. What this demonstrates is the ability for sea level to respond to climate warming at a speed that matches the upper end of IPCC projections for the 21st century.
Sea level in the past closely followed the changes in polar temperatures recorded by ice cores. This connection provides another way to determine the possible trajectory of future sea-level rise. There are uncertainties in this approach, but the observed relationship between temperature and sea level since the 1880s indicates that the IPCC’s estimates for future sea-level rise may be too low. Projected warming for the coming century points to the possibility that sea level could rise by as much as 1.9 metres by 2100.
The potential for rapid changes in ice melt and loss in Antarctica presents an enormous challenge for Australia’s efforts to plan adequately for rising sea levels. Scientists will continue to unlock the clues that Antarctica’s vast ice sheets contain about her past. This will provide a long-term context that is critical to our understanding of the changes we are now seeing – and those that lie ahead for Antarctic ice.
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Postscript: In May 2014 two studies reported that the collapse of the West Antarctic Ice Sheet is now unstoppable. Writing in The Observer, NASA’s Eric Rignot – lead author of one of these studies – explained the role of stronger westerly winds circling around Antarctica in this process, ‘caused by a world warming faster than a [mostly] cooling Antarctica’. (Research shows that large parts of Antarctica are not yet warming, in contrast to the Antarctic Peninsula that is warming very quickly.) ‘Nerilie Abram and others have just confirmed that the westerlies are stronger now than at any other time in the past 1000 years and their strengthening has been particularly prominent since the 1970s as a result of human-induced climate warming,’ he wrote. ‘Model predictions also show that the trend will continue in a warming climate. What this means is that we may be ultimately responsible for triggering the fast retreat of West Antarctica.’
A short walk in the Australian bush
They’re taking over!
They’re taking over! The jellyfish move in
Tim Flannery
It’s become fashionable to keep jellyfish in aquariums. Behind glass they can be hypnotically beautiful and immensely relaxing to watch. Unless we are enjoying them in this way, we usually give little thought to the creatures until we are stung by one. Jellyfish stings are often not much more than a painful interlude in a seaside holiday – unless you happen to live in northern Australia. There, you might be stung by the most venomous creature on Earth: the box jellyfish, Chironex fleckeri.
Box jellyfish have bells (the disc-shaped ‘head’) around a foot across, behind which trail up to 550 feet of tentacles. It’s the tentacles that contain the stinging cells, and if just six yards of all that tentacle contact your skin, you have, on average, four minutes to live – though you might die in
just two. Seventy-six fatalities have been recorded in Australia since 1884, and many more may have gone misdiagnosed or unreported.
In 2000 a somewhat less venomous species of box jellyfish, which lives further south, threatened the Sydney Olympics. It began swarming at the exact location scheduled for the aquatic leg of the triathlon events. The Olympic Committee considered many options, including literally sweeping the course free of the menace, but all were deemed impractical. Then, around a week before the opening ceremony, the jellyfish vanished as mysteriously as they had appeared.
Most jellyfish are little more than gelatinous bags containing digestive organs and gonads, drifting at the whim of the current. But box jellyfish are different. They are active hunters of mediumsized fish and crustaceans, and can move at up to twenty-one feet per minute. They are also the only jellyfish with eyes that are quite sophisticated, containing retinas, corneas, and lenses. And they have brains, which are capable of learning, memory, and guiding complex behaviours.
The Irukandjis are diminutive relatives of the box jellies. First described in 1967, most of the dozen known species are peanut- to thumb-sized. The name comes from a North Queensland Aboriginal language, the speakers of which have known for millennia how deadly these minuscule beings can be. Europeans first learned of them in 1964 when Dr Jack Barnes, who was trying to track down the origin of symptoms suffered by swimmers in Queensland, allowed himself to be stung by one. With nobody attending but a lifeguard and his 14-year-old son, he was lucky to survive.
It’s now known that the brush of a single tentacle is enough to induce ‘Irukandji syndrome’. It sets in 20 to 30 minutes after a sting so minor it leaves no mark, and is often not even felt. Pain is initially focused in the lower back. Soon the entire lumbar region is gripped by debilitating cramps and pounding pain – as if someone is taking a baseball bat to your kidneys. Then comes the nausea and vomiting, which continues every minute or so for around 12 hours. Shooting spasms grip the arms and legs, blood pressure escalates, breathing becomes difficult, and the skin begins to creep, as if worms are burrowing through it. Victims are often gripped with a sense of ‘impending doom’ and in their despair beg their doctors to put them out of their misery.
It’s difficult to know how many victims the Irukandji have claimed. The extreme high blood pressure that often kills is hardly diagnostic. Many deaths have doubtless been put down to stroke, heart attack or drowning. There is some evidence that the problem is growing: Irukandjis have recently been detected in coastal waters from Cape Town to Florida.
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The box jellies and Irukandjis are merely the most exotic of a group of organisms that have existed for as long as complex life itself. In Stung! On jellyfish blooms and the future of the ocean, biologist Lisa-ann Gershwin argues that after half a billion years of quiescence, they’re on the move:
If I offered evidence that jellyfish are displacing penguins in Antarctica – not someday, but now, today – what would you think? If I suggested that jellyfish could crash the world’s fisheries, outcompete the tuna and swordfish, and starve the whales to extinction, would you believe me?
Jellyfish are among the oldest animal fossils ever found. Prior to around 550 million years ago, when a great diversity of marine life sprang into existence, jellyfish may have had the open oceans pretty much to themselves. Today they must share the briny deep with myriad creatures, and with machines. It’s not just the wildlife they’re worrying. In November 2009 a net full of gigantic jellyfish, the largest of which weighed over 450 pounds, capsized a Japanese trawler, throwing the three-man crew into the ocean. But even mightier vessels have been vanquished by jellyfish.
On 27 July 2006, the USS Ronald Reagan, then the most modern aircraft carrier in existence, was docked in the port of Brisbane. New Zealand had earlier banned the entry of nuclear-powered ships, and many Australians felt it might be prudent to follow their lead. So when the commander of US Naval Air Forces announced that an ‘acute case of fouling’ had afflicted the giant vessel, people took notice. Thousands of jellyfish had been sucked into the cooling system of the ship’s nuclear power plant, forcing the closure of full onboard capabilities. Newspapers ran the headline ‘Jellyfish take on US warship’. Local fire crews were placed on standby, and the citizens of Brisbane held their collective breaths as the battle between the navy and the jellyfish raged. In the end, the jellyfish proved too formidable, and the ship was forced out of port.
Even nations can be affected by the power of the jellies. On the night of 10 December 1999, 40 million Filipinos suffered a sudden power blackout. President Joseph Estrada was unpopular, and many assumed that a coup was under way. Indeed, news reports around the world carried stories of Estrada’s fall. It took 24 hours before the real enemy was recognised: jellyfish. Fifty truckloads of the creatures had been sucked into the cooling system of a major coal-fired power plant, forcing an abrupt shutdown.
Japan’s nuclear power plants have been under attack by jellyfish since the 1960s, with up to 150 tons per day having to be removed from the cooling system of just one power plant. Nor has India been immune. At a nuclear power plant near Madras, workers removed and individually counted over four million jellyfish that had become trapped on screens placed over the entrances to cooling pipes between February and April 1989. That’s around 80 tons of jellyfish.
As Gershwin says, ‘Jellyfish have an uncanny knack for getting stuck … Imagine a piece of thin, flexible plastic wrapper in a pool, where it can drift almost forever without sinking, until it gets sucked against the outflow mesh.’ Chemical repellents don’t work, nor do electric shocks, or bubble curtains, or acoustic deterrents. In fact even killing the jellyfish won’t work as, dead or alive, they still tend to be sucked in. And everyone from concerned admirals to the owners of power plants that lose millions of dollars with each shutdown have tried very hard to deter them.
Salmon swimming in pens can create a vortex that sucks jellyfish in. Tens of thousands of salmon can be stung to death in minutes, and repeated attacks can kill hundreds of thousands of the valuable fish. But those losses are small compared with the financial devastation jellyfish have inflicted elsewhere. Would you believe, Gershwin asks, that ‘a mucosy little jellyfish, barely bigger than a chicken egg, with no brain, no backbone, and no eyes, could cripple three national economies and wipe out an entire ecosystem’? That’s just what happened when the Mnemiopsis jellyfish (a kind of comb jelly) invaded the Black Sea. The creatures arrived from the east coast of the US in seawater ballast (seawater a ship takes into its hold once it has discharged its cargo to retain its stability), and by the 1980s they were taking over. Prior to their arrival, Bulgaria, Romania and Georgia had robust fisheries, with anchovies and sturgeon being important resources. As the jellyfish increased, the anchovies and other valuable fish vanished, and along with them went the sturgeon, the long-beloved source of blini toppings.
By 2002 the total weight of Mnemiopsis in the Black Sea had grown so prodigiously that it was estimated to be ten times greater than the weight of all fish caught throughout the entire world in a year. The Black Sea had become effectively jellified. Nobody knows precisely how or why the jellyfish replaced the valuable fish species, but four hypotheses have been put forward.
The first is that stocks of anchovy, which compete with the jellyfish, collapsed because the jellyfish ate their eggs and young. A second is that jellyfish ate the same food as the anchovies, and starved them. A third is that overfishing left more food for the jellyfish, and the fourth is that climate change caused a decline in plankton or promoted a jellyfish bloom. There may be a little truth in all four of these ideas. But one thing is clear. In the end, Mnemiopsis was controlled, and then only partially, by the accidental introduction of another comb jelly. Beroe has tooth-like structures that allow it to eat Mnemiopsis. Only a jellyfish, it seems, can halt a jellyfish invasion.
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Jellyfish continue to pop up in unusual places, and more often
than not trouble is not far behind. Around 2000, the Australian spotted jellyfish was noticed in the Gulf of Mexico. It had presumably arrived in ballast water. These jellyfish can weigh up to 15 pounds, and by August 2000 a plague of them covered around 60 square miles. Their consumption of fish eggs, fish larvae and other plankton was far greater than could be sustained. They ate ten times more fish eggs than was typical for the area. And they had a sneaky way of catching plankton. They jellified the surrounding waters with a kind of foam that slowed the plankton down, making them easier to catch.
Then the Gulf experienced Hurricane Katrina and the oil spill of 2010. Fish and prawn numbers plummeted, but the Australian spotted jellyfish kept going from strength to strength. By 2011 it had shown up in the western Mediterranean, and more than ten people a day were being stung, forcing the closure of tourist beaches at the height of the season. It’s recently been spotted off Israel and Brazil.
From the Arctic to the equator and on to the Antarctic, jellyfish plagues (or blooms, as they’re technically known) are on the increase. Even sober scientists are now talking of the jellification of the oceans. And the term is more than a mere turn of phrase. Off southern Africa, jellyfish have become so abundant that they have formed a sort of curtain of death, ‘a stingy-slimy killing field’, as Gershwin puts it, that covers over 30 000 square miles. The curtain is formed by jelly extruded by the creatures, and it includes stinging cells. The region once supported a fabulously rich fishery yielding a million tons annually of fish, mainly anchovies. In 2006 the total fish biomass was estimated at just 3.9 million tons, while the jellyfish biomass was 13 million tons. So great is their density that jellyfish are now blocking vacuum pumps used by local diamond miners to suck up sediments from the sea floor.